Photometer



April 4, 1939. E. T. TURNEY 2,153,165

' PHOTOMETER Fi led May 10, 1938 INVENTOR. flagella ZTanmgy,

BY Ww TTRN.

. Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE Application May 10,1e: 32:31). 206,981

ZCIaims.

The invention herein disclosed relates to photometers.

, Special objects of the invention are to provide a relatively simple,inexpensive and atthe same time a. thoroughly practical device, whichwill show instantly and accurately the proper exposure and which will beof a small compact form, adapted to be easily and conveniently carriedabout.

The foregoing and other desirable objects are attained by the novelfeatures of construction, combinations and relation of parts hereinafterdescribed, illustrated in the accompanying drawing'and broadly coveredin the claims.

The drawing accompanying and forming part of the specificationillustrates one'practical embodiment of the invention. The structurehowever may be variously modified and changed, all within the trueintent and broad scope of the 20 claims.

Fig. .1 is a front view of the device and Fig. 2 is a rear view of thesame.

Fig. 3 is an enlarged and partly broken view of the base portion of thearticle, with the cover 25 removed.

Fig. 4 is a longitudinal sebtional view on sub w stantially the planeof'line 4-4 of Fig. 1. Fig. 5 is a broken sectional detail of the switchmechanism as on substantially the line 5-5 of Fig.3.

In the present invention, a proper exposure is instantly ascertained byregulating the intensity of a standard light to match existing lightconditions and then comparing the reading of the 35 regulator with anexposure scale, laid off in units corresponding to the units ofregulation or adiustment of the standard light.

In the illustration, the standard light 'is provided by a small lampbulb 'i, Fig. 4, enclosed 40 within a case and placed to illuminate ascreen which is exposed to surrounding light. The light screen is shownas composed of a color filter 8,

and a diffusing disc 9 of frosted glass or the like, these beingconfined between aperture defining 45 'plates or washers i0, H, in'front and back of the same,,within a tube l2, surround ng the bulb. Thislight tube is shown as supported at the back by a sleeve i3, set in thefront cover it, of the casingand a telescopically related viewing tube50 I5, is shown as slidingly interposed between'this outer tube i3 andthe inner light tube l2.

The electrical energy for the lamp is provided in the illustration bytwo dry cells i6, i6, removably held in the terminal clips l1, l8, i9,20,

'of the other dry cell.

The circuit may be traced from the upper clip l'l, through connectingstrip 2!, to center terminal 22, or the lamp socket and from the screwterminal 23 of the lamp socket by wire 24, to the resistance wire 25 ofa current compensating reg- 5 ulator, thence by the brush 26 and spindle21,01 said regulator and strap 28, to the upper clip l9, From the lowerclip 20, of said second dry cell, the circuit is completed by connection29, to resistance wire 30, of the cali- 10 brating regulator and whichlatter has a brush 3 I and a spindle 32, which-at the back is engaged bya'spring strip 33, to which is connected one end of a spring switchcontact 34, which can be depressed by button 35, into engagement withthe base of the other, lower dry cell clip 13.

The spindle of the light intensity regulator is shown as carrying afinger disc 36, calibrated at 3], for registry with an index 38.

Similarly, the spindle 21, of the balancing resistance is shown ashaving a thumb tum' 39, with a line or pointer Ml, which may beassociated with a scale or simple index mark 4|.

The markings on the scale 31, of the regulator are calibrated to matchthe exposure values of a scale such as illustrated at 42, Fig. 2,located on the back or some other conveniently readable position on thecasing.

In the present illustrated embodiment of the invention all parts, of thedevice except the light tube and telescopic extension are mounted on thebase or back 43, of the instrument case. Thus as shown in Fig. 4, thefront of the case is simply a hollow cover fitting over a shoulderedportion 44, oi. the base, removably rtained by spring clips 45, 46, andhaving openings 41, 43, d9, 50, of a size to pass the thumb turns orbuttons 39, 3t, 35, respectively.

The instrument is first standardized, as when inserting new dry cells,by comparison with a known light source such for example as a 40 wattelectric lamp. This is accomplished by exposing the light screen to thestandard light source and then adjusting the knob 39, of thecompensating resistance until the instrument light is no longer apparentthrough the screen, when the switch'button is depressed. This is readilyobservable by pushing the switch button to flash the light and turningthe compensator to trim down the intensity until the light justdisappears and no longer flashes when the button is depressed. Thissimple standardizing step may be performed from time to time to compensate for loss of battery strength. 7

In use the unit is held so that the light screen is exposed to thesurrounding light and at the same time may be readily observed. with theswitch button held in, the main regulator may then be adJusted until theinternal light on the screen just disappears. Then if no light appearswhen the switch button is "flashed one or more times, it will be knownthat the proper adjustment has been reached. The number which thenappears at or nearest the index on the regulating scale is observed, andthen located on the exposure scale 42, on the back of the instrument,

where it shows on the scale the requisite exposure factors for existingconditions, such as extent and duration of exposure.

The battery compensator is in series at all times, so a standardizingadjustment may be made whenever considered necessary or desirable.

The battery drain is so slight that small size cells may be used andthese in the symmetrically balanced relation indicated small space andcanbe quickly removed and replaced when the cover is slipped oil. thebase. The sliding hood or shield it, while not always necessary isdesirable under certain light conditions, where it is diflicult to besure that the adjusted light is balanced with the outside light. Thecolor filter 8, may be green or other tint and if desired, this may bemade relatively removable as by being clamped in place between the endof a liner 5|, within tube i2, and a finishing ring 52, screwed orotherwise removably engaged in the outer end of the tube, thesecooperating to clamp the rings H), II, and interposed screen layers ll,9, between them. Consisting as it does of but few small parts which canbe compactly related, the instrument can be made quite small and lightand of a size to be readily carried in the pocket.

in Fig. 3, occupy r thereby standardize the instrument and sepa-,

rate independently adjustable resistance means in said case andconnected in said battery circuit for regulating the intensity of saidlight source to match surrounding light conditions as observable on saidlight screen.

2. A complete, unitary, portable photometer, comprising a small handcase provided with a light screen, a light source in said case back ofsaid light screen and including an electric lamp and a battery incircuit relation therewith, resistance means in said case and connectedin said battery circuit for balancing the intensity of said lightsourceas appearing at said light screen with the intensity of a standardlight source to thereby standardize the instrument and separateindependently adjustable resistance means in said case and connected insaid battery circuit for regulating the intensity of said light sourceto match surrounding light conditions as observable on said lightscreen, said standardizing means and said second regulating means beingin series relation in said battery circuit and switch means on the casein said battery circuit for flashing the light source as so standardizedand as so regulated to match surrounding light conditions.

EUGENE T. 'I'URNEY.

